Heat pump human washing appliance

ABSTRACT

A residential bathtub or shower is combined with a catch drain or basin below and in proximity with the tub or shower in a unitary structure. Most components of a heat pump are located in the catch basin. A hot water tank is outside of the catch basin but located in the immediate vicinity such as at an end of the tub or above the tub or alongside of the tub. The hot tank includes a heat exchanger that is the heat pump condenser, bringing heat to the hot tank for warming household water. Hot water flows from the tank into the tub or shower for bathing and then drains into the catch basin where heat exchangers remove heat before draining or reuse in flushing a toilet.

CROSS-REFERENCE TO RELATED APPLICATION

The application claims priority under 35 U.S.C. 119(e) from U.S. Provisional Application Ser. No. 63/258,508, filed May 10, 2021.

TECHNICAL FIELD

The invention relates to residential water heating and energy recovery from same.

BACKGROUND ART

Most water heaters in U.S. residences are fueled by natural gas, although electric water heaters have also been widely used where residential electric rates are low. For greener, all-electric buildings, central air-source heat pump water heaters (HPWHs), as direct replacements of conventional gas or electric water heaters, are viewed as the mainstream technology. Heat pumps are more efficient than direct resistance electric heating devices because they use a vapor-compression process to extract some of the required heat from an available source-usually a garage, a basement, or an outdoor closet. HPWHs operate at net efficiencies 50% to 200% higher compared to resistance electric water heaters.

After use in tubs, showers, and often bathroom sinks, heat in warmed water is wasted down the drain. The prior art has recognized that this warm water can be used as a source for a heat pump cycle where the system evaporator extracts heat from the drain water and the condenser heats water stored for washing use. For example, see U.S. Patent Publication 2011/0203786 to Darnell et al. that teaches that waste water heat from a bathtub or sink can be actively transferred to incoming potable water for heating the potable water. Waste water from kitchens and washing machines can also be used as the source to enhance heat pump efficiency, but such water often contains enough residue that filtration is required.

Other than bathtubs and showers, most domestic water heating outlets experience intermittent bursts: a quick handwashing, on/off kitchen sink draws, or multiple short flows in dishwashers and clothes washers. Only bathtubs and showers use continuous hot water draws of three minutes or longer. Draw patterns vary considerably by household. A paper by Parker and Fairey at the Florida Solar Energy Center provides valuable discussion and quantification of how load and hot water use patterns vary: http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-464-15.pdf

U.S. Pat. No. 4,207,752 to Schwarz shows a single device that accepts a waste water stream into a drain basin, uses a heat pump cycle to extract heat from that basin, stores hot water in an integral pressurized tank, and discharges the basin water when the heat extraction cycle is completed.

An object of the invention is heat recovery from waste water in a heat pump associated with residential tubs and showers.

SUMMARY OF DISCLOSURE

The above object has been met with a heat pump human washing appliance (HPHWA) that integrates heat recovery with a tub or shower. This heat pump integration with a tub or shower includes major heat pump components in or near a water catch basin below and integrated with a tub or shower. In other words, a tub or shower drains into a water catch basin immediately below the tub or shower. The catch basin supports a compressor and an evaporator heat exchanger that extracts heat from drain water, with increased heat recovery because of proximity of components. Heat is transferred through a refrigerant circuit to an insulated hot water tank that is part of a built-in appliance.

The catch basin is a wide shallow pan beneath the tub or shower. Several configurations and accessories will be described for the HPHWA, including tubs, showers, a combined tub/shower that also includes a bathroom sink, and a most-integrated version that uses the waste water as grey water for toilet flushing after heat extraction. All share the following attributes and advantages compared to a HPWH in the garage, basement, or outdoor closet:

1. Higher operating efficiency, as a result of extracting heat from a warmer source since bathroom drain water is typically warmer than air in a garage or basement that are alternative heat pump locations.

2. Almost no waste of water or time while waiting for “warm enough” water to arrive at the bathtub or shower, since a hot tank is part of the appliance.

3. Almost no waste of space needed by the HPWH, since the heat pump components are largely integrated into available space.

4. Potential elimination of hot water plumbing when the HPHWA is grouped with a tankless heater at the kitchen sink, a dishwasher that heats water internally, a clothes washer that relies on cold water, and HPHWA connection to a nearby lavatory which saves:

a. Money, by eliminating the materials and labor of an installed, insulated hot water piping system and some drain piping as well

b. Energy, by eliminating thermal losses associated with water flowing and idling in the hot water piping system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified vertical sectional view of a first embodiment of the invention.

FIG. 2 is a side view of a hot tank in the apparatus of FIG. 1.

FIG. 3 is a detailed view of the embodiment of FIG. 1.

FIG. 4 is a plan view of a second embodiment of the invention with hot tank pre-packaged with flexible connecting lines for placement above the tub.

FIG. 5 is a vertical section view of a shower-only embodiment with hot tank integrated into a shower bench seat.

FIG. 6 is an isometric view of an embodiment that includes a reshaped tub with an integrated bathroom sink.

FIG. 7 is a plan view of another embodiment that includes a toilet and unheated tank used to flush the toilet using post-heat extraction wash water.

DETAILED DESCRIPTION

FIG. 1 and FIG. 3 show similar sectional views, with FIG. 1 intended to introduce basic components and FIG. 3 providing more detail. With reference to FIG. 1, a standard bathtub 11, with a sloping drain wall 34 and a less sloping back wall end 35, is installed between framed walls 22 and 23 and above a drain or catch basin 29. Tub 11 does not drain bath water into a sewer but to the drain basin 29 via tub drain 36. The basin temporarily holds hot water from the tub for heat removal. Next to wall 23 is a horizontal axis, cylindrical, pressurized and insulated hot water tank 33 with potable water therein. Tub drain 36 allows water used in bathing to flow by gravity into the drain or catch basin 29 that acts like a large pan for hot water capture and heat removal. A standard 5′ long tub uses a 6′ long space to provide room for the horizontal-axis cylindrical hot water tank 33 in contact with the sloping tub end wall 35. The pre-assembled system may arrive at the job site on a strong plywood bottom sheet 28 as a pre-fabricated human bathing appliance that becomes part of the subfloor if on framed construction, or rests atop concrete in “slab-on-grade” construction. Between the tub bottom and the bottom sheet 28 is the catch or drain basin 29 that collects drainage water from the tub 11 and possibly from a nearby lavatory sink, not shown. The basin 29 slopes from the “reclining end” 35 of the tub 11 toward the drain end 34. The system may include support legs that convey tub occupant loads downward from the tub floor to the sloping basin, with shims aligned under the legs that support the basin and tub on bottom sheet 28.

An electrically driven heat pump removes heat from hot water in the drain basin 29. A vapor compression refrigeration cycle is used for heat transfer in a heat pump. A major component of the heat pump is the compressor 45 shown here as mounted between the tub drain wall 34 and framed wall 22. Hot refrigerant gas from compressor 45 is transmitted to the hot tank 33 where heat is removed using a helical coil wrapped around the tank as shown in FIG. 2.

In FIG. 2 the pressurized hot tank 33, shown with a vertical axis, is seen to have a helical coil 38 wrapped around the tank for good heat transfer that warms water in the tank when the compressor 45 is operating. The coil can be 5/16″ tubing at ½″ spacing on a 27″ long tank that is 17″ in diameter. The helical coil acts as a heat pump condenser heat exchanger that heats the tank 33 when the compressor 45 is operating. The tank is made of stainless steel to avoid corrosion and any need for future replacement. In the preferred embodiment shown, the tank contains 26 gallons of water. With 1.5″ urethane foam insulation all around, the wrapped tank dimensions are 20″ diameter and 30″ long, to fit in the space shown.

In an alternate embodiment, the pressurized hot tank 33 may have an internal helical coil heat exchanger instead of the exterior wrapped helical coil 38 shown in FIG. 2. An internal coil can provide relatively greater heat transfer surface area, but is more expensive than a wrapped external coil, because of both manufacturing challenges and plumbing codes that require double wall separation between refrigerants and potable water. This requirement complicates the design of internal tank domestic water heat exchangers.

In a further alternate embodiment, an atmospheric pressure hot tank, not necessarily cylindrical, may be used that includes a condenser heat exchanger to transfer heat from the refrigerant to the tank water, and a load-side, immersed, pressurized heat exchanger that heats domestic water from the hot tank water.

Returning to FIG. 1, cooled gas in the helical coil condenses to a liquid and is then forced through an expansion device 58, such as a capillary tube, seen in FIG. 3, such that the liquid refrigerant flashes to a gas when entering an evaporator twin spiral heat exchanger 51 that surrounds the pump 54 in a sump 50 that is in a recessed region of the drain basin 29 below the tub drain 36. A sensor, such as a conductive switch, tells the pump to turn on when water is in the sump, and off when the sump is empty. Lukewarm gas leaves the evaporator through a gas line to re-enter the compressor 45 and continue the refrigerant flow cycle. After compressor operation has cooled water in the drain basin, the pump 54 discharges the cooled water into the open-top drain pipe 63, which also serves as an overflow to assure that an over-filled basin cannot spill over onto the bath floor. The drain 63 can be an open-top vertical pipe of 1½″ diameter through which water drains through an outlet pipe, not shown, to a tub trap that prevents sewer gas from entering the bathroom.

The drain basin 29 is configured to hold 20% more volume than the hot tank 33, based on calculations showing effective heat pump efficiency at that volume. In the embodiment shown, the 30″ wide×54″ long basin 29 with 5″ high rim can contain 39 gallons of water. The basin is equipped with a glory hole overflow drain 63.

In the more detailed view of FIG. 3, a shower head and flexible supply hose 44 a and tub fill spout 44 b connect the tank outlet 41 through a control valve 42 that mixes hot tank water with cold water from a cold supply line 43 to achieve the desired delivery temperature. Water supplied to the control valve from the tank 33 is replaced by cold water that enters the tank through the bottom inlet 48 from the cold water supply line 46.

The compressor 45 can be located in the curved tub wall corner cavity at the tub drain end. A pipe 55 carries hot, pressurized refrigerant gas from the compressor 45 into the condenser heat exchanger 38 spiral wrapped on the hot tank. As the gas flows through the heat exchanger, it condenses and leaves the heat exchanger through a pipe 57 as a high-pressure liquid entering next an expansion device 58 before entering the flat spiral evaporator heat exchanger 51 which is located in a sunken reservoir or sump 50 integral with the drain basin 29. The spiral evaporator 51 extracts heat from the drained water when the compressor is operating. From the evaporator 51, lukewarm low pressure refrigerant returns to the compressor 45 through line 62.

Basin drainage and reservoir pump-out are important for system operation and maintainability. When wastewater in the drain pan has been sufficiently cooled, the pump 54 operates to discharge water through the line 16 into the overflow 63. The compressor is turned on by command from the controller when water that is warmer than a setpoint is present in the drain pan, and the pump is turned on when the water has been cooled to below the setpoint, as will be further described with reference to the controls table below. In an alternate embodiment, the system may include an automatic wash-down system that uses flat-spray 90-degree nozzles pointed inward at basin corners. A solenoid valve may be activated by the control system to operate the wash-down system after a fixed time period or a fixed number of cycles. Unheated water from the wash-down system can also be the source for startup, makeup, or post-vacation water heating. In these circumstances, without a basin wash-down system, it will be necessary to use either the heat pump cycle with cold water from the fill valve, or electric heat elements in the hot tank 33 to satisfy water heating needs.

A 12″ wide ledge 30 covers the storage tank 33, acting as a seat and also providing additional space for showering in the tub. Where a 2-bath home might have back-to-back bathtubs, a single 20″ diameter by 63″ long tank and single, larger refrigeration system could serve both bathtubs. When the valve 42 is off, a solenoid valve 54 may be opened to add water through an opening 53 into the drain basin 29, as a water source for auxiliary heating during startup or after an idle period between wash cycles, when the hot tank may have cooled off. In FIG. 4 a second embodiment of the invention has a hot tank pre-packaged with flexible connecting lines for placement above the tub, similar to that shown in FIG. 1 except that it does not require floor area for the tank. Therefore, it is more appropriate for retrofit applications in replacement of an existing tub. The insulated hot water tank 33 is a vertical cylinder located above the tub. The tank 33 is connected by flexible lines, not shown, namely 2 refrigerant, 1 cold water, 1 sensor wire. In this version the single 25-gallon tank is 13.5″ diameter by 42″ long, pre-insulated with an attractive insulative cover 81 designed for structural fastening to the wall framing. The compressor is hidden in the tub corner under the tank, and the basin is now the full footprint of the tub. The shower head 82 is part of the insulated tank assembly, which for packing and shipping fits into the tub basin. In a third version, not shown, a similar tank, but larger diameter and shorter, fits up against the ceiling, with horizontal tank axis, above the fill end of the tub. In both these cases, for storage and shipping, the flexible connecting tubes and wires may be pre-coiled in the tub basin around the tank. A vertical cosmetic cover can be provided for hiding these lines in the wall corner.

In FIG. 5 a vertical section view of a shower-only embodiment has a hot tank 33 integrated into a shower bench seat 25. The tank 33, condenser 38, and compressor 45 are located beneath a removable bench seat 25 and supported on the basin 29 which rests on the subfloor bottom sheet 28. Immersed in the basin water is the evaporator 51, which receives evaporating liquid refrigerant from the expansion device 58 through tubing 57 from the condenser 38. Again, a tube delivers hot refrigerant gas from the compressor 45 to the condenser 38. Flexible, pre-plumbed lines that are coiled for transport can be placed in the wall framing 22, delivering hot and cold water to the mixing control 95 and then upward to the showerhead 82 through the piping line 94. Used shower water drains through a screen 93 into the basin 29.

FIG. 5 shows an alternate mixing strategy with a lift valve rather than a pump. After heat extraction, a normally-closed lift valve 96 is opened on command from the controller, by an actuator 97. Drainage from both the overflow, not shown, and the lift valve flows into a P-trap, not shown below the subfloor 28. The trap prevents sewer gases from entering the basin and bathroom above.

FIG. 6 shows a more complete built-in appliance with a re-shaped tub and an integrated bathroom sink. Components common to all embodiments are not shown in FIG. 6, including all refrigeration components, the basin, the pump, and the overflow. The shaped tub 140, which is removable from the overall assembly 111 for access to the basin and its contained components, is shaped for greater comfort and reduced water volume compared to standard tubs. The bather's torso fits in the widened, deeper end where the drain is, with the bather's feet at the narrow end. A further embodiment, not shown here, includes a raised narrow end with higher, near-horizontal leg rest, for greater comfort and further reduced water volume. The sink 141 allows the insulated hot tank 143 to be placed beneath it, accessed through a hinged panel 148. The controller 142 may allow selection of a bath or shower function, desired delivery temperature, drainage control and other user selectable items. This embodiment is designed to fit within a 30″×60″ framed alcove. The sink 141 with its control features and water supply may be a separate element that for shipping and handling fits into the tub recess but has flexible lines all pre-connected to minimize field labor. This tight packing would allow the delivered package to fit (on edge) through doorways as narrow as 28″. The sink drains into the under-tub basin, and its waste water also becomes a source for the water heating cycle. The tub has no connections to the basin below but is integrated therewith. Waste water from both the main drain and the overflow drain flows into the basin. FIG. 6 also shows other components that pack for delivery in the tub recess, including chrome vertical support pipes 144, the showerhead support pipe 146, the showerhead 147, and curtain support rod 145. The vertical elements slide into prepared sleeves in the base assembly, and the showerhead support pipe connects with “push-fit” connectors into the sink assembly. Also shown are pull-out drawers 149 that take advantage of available space.

In the embodiment of FIG. 7, a low-profile toilet with an oversized tank, used to flush the toilet using post-heat extraction waste water, are included to complete a full bath fixture set. Only the added features are labelled, including the compressor 45 located at floor level between the hot tank 33 and the added toilet seat and bowl 155. The pump 54 sends water from the sump, again a sunken section of the basin through a pipe 152 and an accessible filter 156 into an uninsulated, atmospheric toilet tank 153. This tank, approximately 15″ wide by 21″ long by 18″ deep, sits entirely above the water level of the toilet bowl, contains more than 20 gallons of flush water, and has a removable lid, similar to typical toilet tanks except for its larger size and lightweight polymeric design. The top of the toilet tank 153 is approximately level with the sink 141. The toilet system, preferable using the 0.8 gallons per flush technology of the Niagara Stealth toilet, holds enough water for 25 flushes. When the tank 153 is full, it can overflow through the line 154 shared with the flush valve discharge into the toilet bowl 155, which then overflows through its integral P-trap, just as any toilet bowl would if it had a leaky fill valve. Note that the toilet tank 153 overhangs the narrow, shallow tub end, but does not interfere with bathing or shower space.

With this design, the toilet trap becomes the only trap needed for the entire bathroom, and it is integral with the appliance. For toilet operation when recent washes have not kept the tank 153 adequately full, there are two tank re-filling options. The least expensive option uses the vacation heating cycle that adds water to the under tub basin through a valve and basin inlet. The compressor can operate concurrently to heat the hot tank 33, since without recent sink and/or shower/tub use, the hot tank temperature might need boosting. The second tank refill option, not shown, would add a float valve in the tank 153, connected to the cold water supply, where the float valve maintains a minimum water level, adequate for one or 2 toilet flushes.

HPHWA operation is managed by the user and by a controller. User controls involves turning a mixing valve handle from cold to hot, flipping a toggle switch that opens a fill solenoid valve, and then adjusting the mixing valve to achieve a comfortable water temperature. At the end of each shower or tub-fill, the user switches the solenoid fill valve off and returns the mixing valve to its cold position. The controller is connected to temperature sensors in the tank and basin, respectively; and to two basin water level sensors, one lower and one upper. When the tank temperature sensor reading is below the controller setpoint and the lower water level sensor indicates that there is no water in the sump, the controller will either activate the tank heat elements, if present, or open the fill valve to add water to the basin and sump, depending on makeup heat strategy to achieve the desired hot tank storage temperature. When the tank sensor reading is below the setpoint and the lower water level sensor indicates that there is water in the sump, the compressor turns on to extract heat from water in the basin and transfers it to the tank, until the tank temperature plus a hysteresis buffer is achieved. When the basin temperature sensor reading falls below an upper setpoint, typically cooler than surrounding air, for example 55 degrees F., the controller will either turn on the pump or open the drain valve, depending on drainage design, until sump water temperature rises again to the upper setpoint. If the basin temperature sensor drops below a lower setpoint, for example 50 degrees F., the controller will disable the compressor until water temperature rises. In simple terms, the compressor operates when there is heat to be extracted from basin water, and the pump or drain operates when basin water has been cooled to a point that heat pump efficiency is reduced below a desired level. A water heating cycle ends when the last accessible cooled water batch is pumped or drained from the sump.

The upper water level sensor is a safety/overflow protection device that tells the controller to disable the fill solenoid valve and activate an alarm, since water at this high level in the basin indicates that the drainage mechanism has malfunctioned. An optional appliance control feature is a wireless network connection that allows an outside entity such as an electric utility or a regulatory body to control system-wide electrical loads. In this mode, waste water would remain in the basin until utility loads were reduced. This would reduce efficiency somewhat since water in the basin would cool during the wait.

A table showing operational sequences is below.

Sensors in Basic Unit of FIGS. 1-6

Temp of hot tank, temp of sump, low water sensor, high water sensor

Hot tank has low limit and high limit set

Solenoid allows supply water flow.

Complete Unit of FIG. 7: Add toilet tank low water limit.

Operational Sequence in Basic Unit of FIGS. 1-6

User sets mixing valve, turns on solenoid, bathes or showers

Water sensed in sump, compressor turns on

Sump water temp drops to lower limit, pump turns on

Sump water temp rises an increment, pump turns off

Bather turns mixing valve to cold and fill valve off

Heat cycle continues until water is gone, then pump and compressor turn off

If hot tank needs more, solenoid opens for set time to start backup cycle

Normal tank heat cycle proceeds

Backup cycle continues until hot tank is satisfied.

(Safety) If basin water level too high, solenoid disabled, alarm flashes.

Operational Sequence in Complete Unit of FIG. 7

User sets mixing valve, turns on solenoid, bathes or showers

Water sensed in sump, compressor turns on

Sump water temp drops to lower limit, pump turns on

Sump water temp rises an increment, pump turns off

Bather turns mixing valve to cold

Heat cycle continues until water is gone, then pump and compressor turn off

If hot tank needs more, solenoid opens for set time to start backup cycle

Normal tank heat cycle proceeds

Backup cycle continues until hot tank is satisfied.

If toilet tank water level low and hot tank satisfied, solenoid opens and pump operates

(Safety) If basin water level too high, solenoid closes, alarm flashes. 

What is claimed is:
 1. A human washing appliance with heat capture from water used in human bathing, comprising: a. a tub or shower fixture; b. a shallow basin immediately below the tub or shower in a position receiving bathing water from the tub or shower by gravitational flow; c. a tank containing heated water plumbed to supply water to the tub or shower fixture; and d. an integral heat pump circuit having a compressor, a condenser heat exchanger associated with the tank that heats water in the tank, an evaporator heat exchanger in the basin that extracts heat from water in the basin, and an expansion device that restricts flow from the condenser heat exchanger to the evaporator heat exchanger.
 2. The appliance of claim 1 wherein the tank is cylindrical and contains pressurized water.
 3. The appliance of claim 2 wherein the tank is metallic and has an external condenser heat exchanger in contact with the outer tank surface.
 4. The appliance of claim 1 wherein the evaporator heat exchanger comprises at least one flat spiral plumbed within the basin.
 5. The appliance of claim 1 wherein the tank is below a seat used with the tub or shower.
 6. The appliance of claim 1 further having a hand wash basin that receives water from the tank and discharges wastewater into the basin.
 7. A human washing appliance with heat capture from water used in human bathing comprising: a. a planar support bottom sheet; b. a shallow basin mounted on the support sheet; c. a tub or shower fixture connected to a pre-plumbed tank wherein the shallow basin receives waste water from the tub or shower fixture by gravitational flow; d. an integral heat pump circuit including a compressor, a condenser heat exchanger that heats water in the tank, an evaporator heat exchanger that extracts heat from water in the basin, and an expansion device that restricts flow from the condenser heat exchanger to the evaporator heat exchanger; and e. discharge means for removing water from the basin after heat extraction.
 8. The appliance of claim 7 wherein the support bottom sheet is incorporated into a sub-floor of a building.
 9. The appliance of claim 7 wherein the basin includes an automatic wash-down system using pressurized water that can be used as a supplementary heat source for the evaporator heat exchanger.
 10. The appliance of claim 7 wherein the tank includes one or more electric heating elements to heat water in the tank to a desired temperature when insufficient waste water is available for heat extraction.
 11. The appliance of claim 7 wherein the discharge means is a gravity drain opening.
 12. The appliance of claim 7 wherein the discharge means is a pump.
 13. The appliance of claim 12 further having a toilet with a flushtank that receives waste water from the basin.
 14. The appliance of claim 13 having only two plumbing connections including a cold water supply in and a toilet drain out.
 15. The appliance of claim 7 wherein a tub has a shape wherein a bather reclines in a wider deep end with legs and feet in a much narrower opposite end.
 16. The appliance of claim 7 that includes a controller to operate the compressor and the discharge means.
 17. The appliance of claim 16 wherein the controller operates the compressor when water in the basin is warmer than a first setpoint, and operates the discharge means when water in the basin is cooled below a second setpoint.
 18. The appliance of claim 16 wherein the controller includes a solenoid fill valve that a bather manually switches open, and that closes when water level in the basin reaches a high level. 